1. Field of the Invention
This invention relates to a gas sensor for detecting a concentration of a specific component, for example, a NOx component of a measurement gas. An example of the measurement gas is an exhaust gas emitted from an internal combustion engine.
2. Description of the Related Art
In general, a NOx concentration sensor is necessary to implement feedback control of an automotive engine to reduce NOx emission therefrom. A NOx concentration sensor located at a point in an engine exhaust passage downstream of a NOx-processing catalytic converter can be used in a system for determining whether or not the catalytic converter has significantly deteriorated.
A prior-art NOx concentration sensor has characteristics which tend to be affected by a temperature change.
It is an object of this invention to provide an improved gas sensor.
A first aspect of this invention provides a gas sensor comprising a body having a measurement-gas chamber and a reference-gas chamber, the measurement-gas chamber being supplied with a measurement gas, the reference-gas chamber being supplied with a reference gas; a detecting cell provided in the body and including (1) a solid electrolyte member, (2) a measuring electrode provided on the solid electrolyte member and facing the measurement-gas chamber, and (3) a reference electrode provided on the solid electrolyte member and facing the reference-gas chamber; and a heater portion for heating the detecting cell, the heater portion including (1) a substrate, (2) a heating member provided on the substrate, and (3) a high-voltage-side lead portion provided on the substrate and electrically connected to the heating member; wherein the substrate has a first surface and a second surface opposite to each other, and the first surface of the substrate faces the body, and wherein the heating member extends on the first surface of the substrate, and approximately the entire length of the high-voltage-side lead portion extends on the second surface of the substrate.
A second aspect of this invention is based on the first aspect thereof, and provides a gas sensor wherein the heater portion further includes a low-voltage-side lead portion provided on the substrate and electrically connected to the heating member, the low-voltage-side lead portion extending on the first surface of the substrate.
A third aspect of this invention is based on the second aspect thereof, and provides a gas sensor wherein the heater portion further includes an insulating member provided on the substrate and having an opening of a negative pattern with respect to the heating member and the low-voltage-side lead portion, and wherein the heating member and the low-voltage-side lead portion fit in the opening in the insulating member.
A fourth aspect of this invention provides a gas sensor comprising a body having a measurement-gas chamber and a reference-gas chamber, the measurement-gas chamber being supplied with a measurement gas, the reference-gas chamber being supplied with a reference gas; a detecting cell provided in the body and including (1) a solid electrolyte member, (2) a measuring electrode provided on the solid electrolyte member and facing the measurement-gas chamber, and (3) a reference electrode provided on the solid electrolyte member and facing the reference-gas chamber; and a heater portion for heating the detecting cell, the heater portion including (1) a first substrate, (2) a heating member provided on the first substrate, (3) a high-voltage-side lead portion provided on the first substrate and electrically connected to the heating member, (4) a low-voltage-side lead portion provided on the first substrate and electrically connected to the heating member, and (5) a second substrate covering the heating member; wherein the first substrate has a first surface and a second surface opposite to each other, and the first surface of the first substrate faces the body, and wherein the heating member extends on the first surface of the first substrate, and the high-voltage-side lead portion extends on the second surface of the first substrate.